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Olmstead Phys 528 21Jan11 "#!"$ ($"# 7 (% $#890 +,"# " $"#% ,##. 0 $## : (# #" !#% 44 >AE " "#!, : (" !$+, 44 >>E ) $ (" 5",6/ !" D 5!6/ ) $ (" 5"6/ )"$ : (" # 56/ % ,"$" $ (" 5")6 21 # !! $ " ! #$;(*1( A@@ CDB4@>@? 0 '!033($,1*#$1(3#$ 9 , $ #!! ( $ % #$"$# Olmstead Phys 528 21Jan11 o "! o o o ! o # ! Faculty Expertise NT Dual PhD Program Graduate Fellowships User Facility National Infrastructure Joint Institutes Societal Impact Research Centers Director: Francois Baneyx Education and Outreach: Ethan Allen Lab Manager: Alec Pakhomov NT PhD Program: Marjorie Olmstead Founded 1997 www.nano.washington.edu New Molecular Engineering and Science Building 2012 “Cleantech and Biotech” Olmstead Phys 528 21Jan11 % !( 6+ ( — & %!( ( !! — & .0&!/ ( ! $ — & ? ! ! ! $ ! ! !( 1!* * %* %* * %* * ( ( %! ,2 7+ % — !%! ! ! — % ! ! ' 3 !( 8+ !" — @ 6 %! &- !! 9+ 0&! % — @ 8 %* @ 7 ' !! :+ !( — $ @ ;5> * @ 9 %! Olmstead Phys 528 21Jan11 General 9% Astro/Gravity 6% Particle/ Beams 10% Nuclear 6% Atomic 9% Chemical/ Laser 8% Nonlinear 3% Fluids 8% CM,Materials 17% Polymer/Bio 8% Applied 5% Compute/ Instrument 5% plasma 6% APS Fellows Elected in 2010 "
Transcript of 7 ( % $#890 +, # $ #% ,# #.faculty.washington.edu/wilkes/528/presentations/Olmstead... · 2011. 1....
Olmstead Phys 528 21Jan11 Olmstead Phys 528 21Jan11
o
o
o
o
o
Faculty
Expertise
NT Dual PhD
Program
Graduate
Fellowships
User Facility
National
Infrastructure
Joint
Institutes
Societal
Impact
Research
Centers
Director: Francois Baneyx Education and Outreach: Ethan Allen
Lab Manager: Alec Pakhomov NT PhD Program: Marjorie Olmstead
Founded 1997
www.nano.washington.edu
New Molecular Engineering and Science Building 2012“Cleantech and Biotech”
Olmstead Phys 528 21Jan11
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—
—
—
—
—
—
— Olmstead Phys 528 21Jan11
General9%
Astro/Gravity6%
Particle/Beams10%
Nuclear6%
Atomic9%
Chemical/Laser8%
Nonlinear3%
Fluids8%
CM,Materials17%
Polymer/Bio8%
Applied5%
Compute/Instrument
5%
plasma6%
APS Fellows Elected in 2010
Olmstead Phys 528 21Jan11 Olmstead Phys 528 21Jan11
Compiled by D. Cobden
Olmstead Phys 528 21Jan11
How Big is a Nanometer?
10 meters
www.nano.gov
10 millimeters
10 micrometers
10 nanometers ~ 50 atoms
Olmstead Phys 528 21Jan11
Olmstead Phys 528 21Jan11 Olmstead Phys 528 21Jan11
COPIES: http://faculty.washington.edu/olmstd
Olmstead Phys 528 21Jan11 Olmstead Phys 528 21Jan11
R O2 at 1000°C
Olmstead Phys 528 21Jan11 Olmstead Phys 528 21Jan11Villora et al, Applied Physics Letters 92 (2008) 202120
As grown 1017 cm-3
O2 Annealed Insulating
Oxygen vacancy model: Lorenz (1967) Binet (1998) Yamaga (2003)
E.g. Yamaga et al, Phys. Rev. B 68 (2003) 155207
Are oxygen vacancies
really responsible?
Sample Carrier concentration
Us (2010) In Vacuum
In Air
Si
Villora (2008)
Olmstead Phys 528 21Jan11
Not consistent with VO model
10-5
10-4
10-3
10-2
10-1
100
101
Conducti
vit
y
2 4 6
102 4 6
1002
Temperature
b
c
800 °C
Vacuum Anneal
Annealed - c
Annealed - b
Olmstead Phys 528 21Jan11
Ga2O3 (perfect bulk) Ga2O3 (with Vo defect) + (O2) neutral vacancy
Ga2O3 (bulk) Ga2O3 (with Vo defect) + (O2) + 2e- 2+
2+ vacancy
q
Olmstead Phys 528 21Jan11 Olmstead Phys 528 21Jan11
BB
SPV
h = 6 keV
Photoemission Binding Energy
Vs. Intensity
Olmstead Phys 528 21Jan11
+
-
Ch
arge Bulk
Surface
+7 V (sample)
Olmstead Phys 528 21Jan11
+
- Ch
arge Bulk
Surface
EF
(2+/0+)
Olmstead Phys 528 21Jan11
TiOx Ga2O3
Bulk Device: • Length Scale ~ Microns• Time Scale ~ Seconds• Temperature ~ 1000 °C
Nanoscale Device:• Length Scale ~ nanometers• Time Scale ~ microseconds• Temperature ~ 25 °C• Aided by Electromigration
Vacancy – Interstitial
Transport
Olmstead Phys 528 21Jan11
Al2O3 Ga2O3
Olmstead Phys 528 21Jan11 Olmstead Phys 528 21Jan11
33 Olmstead Jan 2011
Optoelectronics Choices
Optical Band Gap vs. Lattice Parameter
• Ga2Se3
– Matched to Si– Non-linear optics– Direct band gap– Anisotropic– Cool growth physics– Useful material??
2 3 4 5 6 7 8
IRV
ISU
V4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Ene
rgy
Gap
(eV
)
4.44.34.24.14.03.93.83.73.6
Hexagonal Plane Lattice Spacing (Å)
GaSe
Ga2Se3GaS
-Ga2S3
Ga2Te3
GaAs
Si
Ge
InP
GaP
ZnSe
ZnS
ZnTe
AlP
InAs
GaSb
AlAs
GaTe
InSe
-Ga2S3
Al2Se3
Intrinsic Vacancies
34 Olmstead Jan 2011
Ferromagnetism in Cr-doped Ga2Se3
Adding Chromium to Ga2Se3
makes it a ferromagnet at
room temperature
Cr-doped
Pure
Si(100):As
E. Yitamben et al, in press PRB
35 Olmstead Jan 2011
Surface morphology (solubility limit?)
Increasing Cr
Concentration 17% 9% 6% 3%
Cr-doped
Pure
Si(100):As Pure
Si(100):As
100 nm
Low Cr Incorporates into Nanorods
Higher Cr Nucleates Islands
Islands are Cr-rich
New Compound?
Scanning Auger Microscopy
36 Olmstead Jan 2011
vacuum level
1s 2s 2p
3s Excitation
electron
Auger Process
Fills hole Kicked out
electron
Auger Electron
Aftermath of photoemission
Can also be excited by electrons
37 Olmstead Jan 2011
Surface morphology (solubility limit?)
Increasing Cr
Concentration 17% 9% 6% 3%
Cr-doped
Pure
Si(100):As Pure
Si(100):As
100 nm
Low Cr Incorporates into Nanorods
Higher Cr Nucleates Islands
Islands are Cr-rich
New Compound?
Scanning Auger Microscopy
38 Olmstead Jan 2011
Ferromagnetism and Morphology
0/X %
Saturation Moment
– T = 300 K H = 5 T
Flat films (6% Cr):
High concentration
Larger than expected
moment:
Msat
(4d)
Msat
(d)~ 3
μsat(islanded) < μ
sat(flat)
μsat4μ
B/ Cr
Cr-doped
Pure
Si(100):As
Pure
Si(100):As
Cr-doped
E. Yitamben et al, in press PRB
39 Olmstead Jan 2011
Photoemission – Electron States
E. Yitamben et al, in press PRB 40 Olmstead Jan 2011
Xray Absorption Fine Structure – Local Geometry
Cr 1s
Cr 4p
Cr 3d
VB
Only if
n(x)=n(-x)
Any
Symmetry
Cr 1s
Cr 4p Cr 3d
VB
Interference Pattern
from Neighboring Atoms
